Since the beginning of time, moments have steadily moved by. However, it was not until much later that they began ticking...

When did human beings realize a need to know the time:

The need to know would likely have originated around yearly events that occurred in specific seasons. The cycle of budding plants in the spring, warmth and plant growth in the summer, harvest in autumn, and the dead, colder season of winter became important knowledge for survival. Once we had mastered the domestication of plants, it became necessary to know when they must be put into the ground and when they must be harvested, in order to get the highest annual yield and sustain the greatest number of people in a community. The observation of this seasonal rotation evolved into an observance of special holy days that represented a supplication for, and celebration of, the earth's bounty. Gradually, in many different cultures and in all corners of the world, people created systems to keep track of a year's worth of time. None were entirely accurate at the beginning, and it took a long time and many different experimentations for them to eventually become as precise as the system we use today.

The orbit of the earth around the sun was the first way people knew to tell any sort of time, long before they even knew the earth was round. The science was beyond their understanding, but the obvious movement of the sun across the sky was unmistakable. The phases of the moon were another way to tell the passing of time. Each new moon represented a segment of time, and an early idea of months came to be. Combine this with the observation of the four seasons, the ebb and flow of rivers, and the change in star constellations, and you come up with the rough span of a year. The only problem was that moon cycles are not exactly equivalent to the number of days in modern-day months, and therefore for a long time there was a lack of consistency from year to year.

What is the definition of a clock:

There are two things a clock must have in order to be defined as such. The first is a regular, constant, or repetitive process or action to mark off equal increments of time. Some examples of this are candles notched in increments, hourglasses that "drip" regular amounts of sand, knotted cords that burn incense, or even the movement of the sun across the sky. The second is a means of keeping track of, and displaying the result of the time measured, like the hands on the face of a watch, or the shadow on a sundial.

In what degrees did time-counting devices progress with technology and necessity:

The first "clocks" that we know about originated in ancient Egypt around 3500 BC. They were called obelisks, and consisted of a tall, thin, oblong form reminiscent of the Washington Monument, constructed of stone. As the sun moved across the sky, the shadow from the obelisk would move at a steady rate, falling across markers laid out on the ground at specific intervals. The idea is similar to the better-known sundial, or the modern clock, where the hands move around the face in a steady motion, hitting markers that designate the hours in a day. However, unlike most modern clocks, time-telling using obelisks was based solely on the movement of the earth around the sun.

By 1500 BC, the Egyptians had designed a much smaller type of clock, the sundial. Essentially a minute replica of the obelisk, a sundial had the added advantages of being portable and accurate to a higher degree. However, the nature of sundials is to rely on the sun's exact position in the sky, and therefore when moved beyond their original latitude and/or longitude, they gave false readings. The other disadvantage of such a clock was that it was incapable of giving any sort of reading whatsoever on cloudy or rainy days, or at night. Even the changing seasonal position of the earth in its rotation around the sun would cause the readings on a sundial to change. At worst, a sundial was only accurate, or useable, half the time, and at best it was a complicated process of deducting the correct time from the location and length of a shadow.

Also starting around 1500 BC, and continuing on until around 500 AD, people were using water clocks, also known as Clepsydras or "water stealers." These worked on the premise that water dripping at a steady rate into, or out of, a vessel created for this purpose would keep track of time. These had the same limitations as hourglasses, which is to say they could keep track of a previously determined amount of time, but they could not tell you which hour of the day it was. Many variations of clepsydras were created, some with very fanciful displays to show the amount of time that had elapsed.

In 600 BC, an astronomical tool called a Merkhet was developed, which allowed people to tell time based on the position of the constellations.

300 BC saw the creation of the Hemicycle, which in essence was half of a sundial. Since 180 degrees of the 360-degree sundial were useless due to the fact that the sun only travels through the sky on one side of the dial, rather than around in a circle above it, the hemicycle was a more efficient design of the same mechanism.

Around 150 BC, another astronomical tool, called the astrolabe, came about. This was a fairly simple mechanism, capable of measuring the angle of certain key stars, like a protractor, but it required the knowledge of some more complicated mathematical equations in order to come up with a result resembling time.

In 30 BC, Vitruvius wrote that thirteen different types of sundials existed throughout Greece, Asia Minor, and Italy. By 900 AD, even pocket sundials were available for the affluent consumer!

In 1300 AD, large verge-and-foliot mechanisms, using weights, were used to run clocks.

1500 saw the invention of spring-powered clocks, which could be miniaturized into pocket-watch size, unlike weight driven clocks. These were a step forward in technology, but they had the problem of the main spring slowly unwinding, causing the watch to keep time at a slower-than-accurate rate. Nevertheless, they were greatly popular.

In 1656, the pendulum clock evolved. Galileo had drawn up a blueprint of such a mechanism several years earlier, after observing the steady properties of a pendulum (a pendulum on a short chain swings at the same rate as one on a much longer chain). However, he did not live long enough to bring this invention to life. The pendulum clock was the first to ever stay accurate to within one minute per day. It allowed seconds to be counted for the first time in history! You can still see the pendulum clock today - a prime example is what we now call the Grandfather Clock.

In 1675, the spring in spring-powered clocks was counterbalanced by a balance wheel, making it much more accurate for longer periods of time. This combination is still used in some watches today.

1761 saw the advent of the Marine Chronometer, which allowed people to tell time from a rolling ship in the middle of the ocean.

In 1855, Greenwich Mean Time (GMT) was born. It was the first time in the history of time-keeping that the entire world agreed. Up until that point, global time was not cohesive. Each longitudinal portion of the earth had its own accepted time, but these times did not take into account those of any other area. When Greenwich, England became widely recognized as the "starting point," it suddenly became possible to understand time in a global sense.

As technology advances, it tends to be possible to do the same thing or better on a smaller and smaller scale. That is the case with quartz clocks, which came about in 1920. Quartz crystal was discovered to have a regular, consistent vibration unique unto itself. Any vibration can be harnessed as a regulator to tick away the seconds, as long as a conversion has been established between the two units of time. In a quartz clock or watch, a tiny quartz crystal vibrates on its own, and is put in contact with a magnet, which switches back and forth between a negative and positive charge in time with the quartz vibration. The change from negative to positive causes a small pinion to move, activating the mechanical hands that you see on the face.

In 1949, smaller technology hit again; the vibration of a single atom was harnessed. The first atomic clock used an atom of ammonia, which had an even more reliable vibration than did a quartz crystal. From 1955 until now, we have used cesium atoms.

In 1967, the second was redefined, based on atomic vibration rather than the movement of the earth.

In 1972, Coordinated Universal Time (UTC) improved upon the atomic clock. UTC runs at the same rate of the atomic clocks, however, when the difference between this atomic time and one based on the earth's movement approaches one second, a one second adjustment - a "leap second" if you will - is made in UTC.

By the year 2002, atomic clocks were keeping time to within 30 billionths of a second per year.

In 2004 we have the advent of the Sunclock Heliochronometer. It is the world's first consumer "sundial" to truly tell accurate time. All of the sundials previously offered through mail order were solely decorative and were useless as keepers of time. The SunClock is the first absolutely correct solar clock custom crafted to match the zip code of the owner's residence. Historically, telling time by the sun has required complicated reference charts and extensive installation procedures. Massive sculptural chronometers can also be exquisitely precise, but remain in the realm of wealthy patrons. The SunClock applies the principles underlying helio-chronometers to create an elegant, easy-to-use, and affordable solar timepiece.

The Evolution of Time Measurement through the Ages
From stone calendars to the atomic age of timekeeping, this illustrated history of time spans the progress of mankind through the ages and its relationship to timekeeping and recording of history.

Clockworks: From Sundials to the Atomic Second
A flash exhibit showing working renditions of common time keeping devices from sandglasses and sundials to spring-driven and quartz clocks each with an article about how each timekeeping device was invented.

The U.S. Official Time
Click on your timezone to see the current time in your part of the United States. Works for territories of the U.S. also.